powerpc/spufs: remove set but not used variable 'ctx'

arch/powerpc/platforms/cell/spufs/inode.c:201:22:
 warning: variable ctx set but not used [-Wunused-but-set-variable]

It is not used since commit 67cba9fd ("move
spu_forget() into spufs_rmdir()")

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20191023134423.15052-1-yuehaibing@huawei.com